Fix a bug to handle the fact that a CPU can send Functional accesses while a sendTimi...

Fix a bug to handle the fact that a CPU can send Functional accesses while a sendTiming has not returned in the call stack.

src/mem/cache/base_cache.cc:
    Sometimes a functional access comes while waiting on a outstanding packet being sent.
    This could be because Timing CPU does some post processing on the recvTiming which send functional access.
    Either the CPU should leave the pkt/req around (so They can be referenced in the mem system). Or the mem
    system should remove them from outstanding lists and reinsert them if they fail in the sendTiming.

    I did the later, eventually we should consider doing the former if that is the correct behavior.

--HG--
extra : convert_revision : be41e0d2632369dca9d7c15e96e5576d7583fe6a